Effect of sodium and potassium level on the absorption of magnesium and other macrominerals in sheep

Abstract

Three mature Suffolk × halfbred wethers were utilized to study the effect of dietary sodium (Na) and potassium (K) level on the absorption of magnesium (Mg), Na, K, calcium (Ca) and phosphorus (P). The sheep were surgically equipped with a rumen fistula and re-entrant cannulae in the proximal duodenum and terminal ileum. Six semi-purified diets were prepared with three levels of sodium and two levels of potassium and constant levels of other elements in all six diets. Mg absorption before the small intestine decreased with increased K and a negative correlation was found between K intake and net Mg absorption before the small intestine. The addition of K to the diet increased fecal Mg, and decreased urinary Mg excretion and apparent absorption of Mg. Increasing K levels in the diet decreased the plasma Mg concentration and there was a negative correlation between K intake and plasma Mg concentration. A significant negative correlation between net Mg absorption before the small intestine and rumen pH was found. The level of Na per se in the diet was not an important factor affecting Mg metabolism but the Na/K ratios in feed and rumen liquor were. Supplementation of K, increased the urinary and fecal Ca excretion while Na in the diet increased the concentration of blood plasma P. No other changes in Ca or P metabolism were observed. K level in the diet depresses Mg absorption and Na can be used in high K diets to counteract the effects of K on Mg absorption.